1. Field of the Invention
The present invention relates to telecommunication systems, particularly to devices for enhancing signal strength in areas that do not received direct line-of-sight transmissions.
2. Description of the Related Art
Cellular devices communicate with electromagnetic waves that utilize radio frequencies (RF). In a communication system, waves are transmitted by a transmitter and received by a receiver. For optimal efficiency, a direct line of sight should exist between the transmitter and the receiver; that is, the receiver should be in the area that is “illuminated” by the transmitter so that the strength of the received signal is maximized.
One of the properties of electromagnetic waves is that as the wavelength gets shorter, the waves propagate similarly to light. Therefore, areas that are not illuminated by a transmitter are in what is known as an RF shadow. If a cellular customer is located within an RF shadow, the strength of the received signal is greatly deteriorated; thus, high-quality reception cannot be expected.
Low signal strength may be mitigated to a certain extent by reflection. If a receiver (i.e., a cellular phone) is within an RF shadow that is physically close to a transmitter, the propagated wave from the transmitter will reflect off of surrounding or ambient objects (e.g., buildings) back to the cellular phone. This is known as local reflection. However, because of the physical characteristics of such ambient objects, the reflected signal will not have the same quality of a directly received line-of-sight signal.
The line-of-sight propagation of cellular communications is particularly obvious in mountainous areas, especially in areas distant from the transmitter where the local reflection does not provide usable signal strength. Other areas where RF shadows are present include urban areas with high-rise buildings, building interiors, and underground facilities.